1. Field of the Invention
The present invention relates to a road vehicle communication method using light and radio and advantageously applicable to a reservation download type of asymmetric communication system. This type of communication system belongs to a family of Road Vehicle Communication (RVC) systems capable of providing automotive vehicles with information services by ROF (Radio On Fiber) , which implements radio communication between the vehicles and roadsides by use of optical fibers.
2. Description of the Background Art
Wired services and wireless services are available with an asymmetric communication system. Wired services use, e.g., ADSL (Asymmetric Digital Subscriber Line) or CATV (Cable Television) Internet while wireless services use communication satellites. ADSL and CATV Internet are implemented by existing metallic telephone lines and exclusive coaxial cables for CATV, respectively. As for wireless services, telephone lines and satellites are assigned to up-going channels (requests for information services) and down-going channels (provision of information services), respectively.
A request for an information service, whether it be wired or wireless, and the provision of the same are effected substantially at the same time at the same location. Locations where information services are available are fixed. The maximum communication rate available on down-going channels is 1 Mbps (megabits per second).
There is an increasing demand for information services that users can receive at destinations or while in movement. To meet this demand and considering the fact that some information services deal with audio, video or similar mass information, environments that allow users to receive services rapidly without any stress are essential.
Wired services are, however, provided only at fixed locations. Likewise, wireless services are received from satellites via fixed antennas, so that communication terminals to receive the services via the antennas are also fixed in place. Further, such information service systems are not feasible for the transmission of mass information because the maximum communication rate is 1 Mbps, as stated earlier.
Moreover, each information service is implemented as an exclusive system independent of the other systems. In addition, information service systems linked to other networks or media have not been reported yet.
It is therefore an object of the present invention to provide a road vehicle communication method capable of providing a mobile station with mass information rapidly when the mobile station reaches a destination or while it is running at high speed.
An RVC method of the present invention allows bothway communication to be held between a mobile station, which sends a request for an information service and receives it, and a central base station and local base stations located at a roadside for sending the information service to the mobile station. The central base station and the local base stations use optical fibers in part of the transmission path thereof for the bothway communication and perform at least one of electric-to-optical conversion and optical-to-electric conversion. The mobile station is caused to send the request for an information service beforehand. In response to the request, the local base station covering the mobile station expected to receive the information service is estimated. When the mobile station lies in a service area to which the local base station estimated is assigned, a control station is caused to provide the mobile station with information corresponding to the information service requested.